RFC: 2 enhancement DIPs that need feedback

[Timon Gehr]

On 5/13/25 11:04, Basile B. wrote:
> On Monday, 12 May 2025 at 23:29:36 UTC, Meta wrote:
>> On Monday, 12 May 2025 at 23:23:27 UTC, Monkyyy wrote:
>>> On Monday, 12 May 2025 at 23:13:23 UTC, Meta wrote:
>>>> Hello, I've been working on a couple different DIPs that propose 
>>>> various enhancements to D.
>>>>
>>>> [...]
>>>
>>> I think dip 2 is far more important, dip 1 has work arounds and I 
>>> dislike the complexity around constructors as is
>>
>> Please leave your feedback in the respective threads I linked. Thank you!
> 
> I'll drop a comment here anyway because it doesn't fit to the DIP 
> section I think.
> 
> D really needs "variable declaration" as expressions. My opinion is that 
> here you are again faced to a special case that the general case, i.e 
> "variable declaration" as expression, would have solved.
> 
> ```d
> (auto a, auto b) = call(); // two VarDeclExp in the LHS
> ```
> ...

No, this syntax would not work just because there would be variable 
declaration as expression. You still need a) tuple literals b) dedicated 
unpacking logic.


> Let me enumerate all the cases we have now. You can exceptionally 
> declare variable as expression in
> 
> - the IfStatement
> - the WithStatement
> - the WhileStatement
> - the SwitchStatement
> 
> and now what is proposed is another case: as tuple element.
> ...

Actually that is not true. The DIP does not propose dedicated tuple 
syntax to be added. It's just about unpacking. Anyway, it's not like 
that blocks work on your vision at all.

> Cant just people open their eyes ? That language construct tends to 
> become a well defined expression.
> 
> A little joke to finish, I occasionally use that thing to count if 
> something new is worth:
> 
> ```d
> printf("for the %dnth time\n", static int count++);
> ```
> 
> Yeah that kind of things work when you have "variable declaration" as 
> expression.

Go ahead and implement it. It's harder, not a simplification. Suddenly, 
whenever you are parsing any expression, you will have to take into 
account the possibility that it is actually a variable declaration. The 
way DMD deals with lvalues is also ill-equipped to allow this to be 
added easily. Furthermore, you now have to do proper scope handling for 
short-circuiting operations.